Question

Yesterday I’ve discovered that Bash provides a means to mark variables as read-only, using the readonly keyword:

readonly hello="hello"
hello="world" # error message, Bash refuses to reassign the variable

This seems like a nice feature, still, I’ve never seen this used in any Bash script. Is there any reason not to use this extensivly? Is it actually portable?

Answer 1

readonly is useful for some variables that are set by bash, for example $UID – non-readonly values like $LOGNAME and $USER are easy for the user to alter.

If you find readonly useful then use it! Not many people use readonly, but don’t let that bother you. Downside – like other variable attributes, readonly attribute is not passed on with an exported variable, unless the child process is another bash.

One use of readonly is to apply it to a function. That’s not widely done, but it solves a support issue of (by mistake) having two functions of the same name, which can be an issue when using functions stored outside the script.

ksh also supports readonly (as an alias).